A lot of researches on silsesquioxane have so far been made, and a large number of reports are present. For example, according to a general remark (non-patent document 1) issued by Baney et al., it is confirmed that an amorphous structure which does not show a fixed structure in addition to a ladder structure, a cage structure and an incompletely condensed structure is present in silsesquioxane. In the present specification, an incompletely condensed structure means a structure in which at least one part of a cage structure is not closed.
Among organosilicon compounds having silanol, the following compounds can be given as publicly known compounds.
Among compounds represented by Formula (4), the compound in which a substituent represented by R4 is cyclohexyl is reported by Brown et al. (non-patent document 2); the compounds in which it is cyclopentyl and cycloheptyl are reported by Feher et al. (non-patent document 3); and the compounds in which it is methyl, ethyl, isobutyl and cyclohexyl are reported by Lichtenhan et al. (patent document 1).

In recent years, the silsesquioxanes represented by Formula (4) having an incompletely condensed structure are commercially available from Hybrid Plastics Inc. of U.S.A., but the kinds thereof are limited.
Among cyclic compounds represented by Formula (5), the compound in which a substituent represented by R5 is cyclohexyl or phenyl is reported by Brown et al. (non-patent document 2 or non-patent document 4), and the compound in which it is isopropyl is reported by Unno et al. (non-patent document 5).

Further, an organosilicon compound of a ladder structure represented by Formula (6) having silanol at an end is reported by Unno et al. (non-patent document 6).

In Formula (6), i-Pr represents isopropyl, and n is an integer of 1 to 4.
However, it has not been known that present is an organosilicon compound of a double decker structure represented by Formula (1) which has silanol and which is provided by the present invention. Accordingly, polysiloxane obtained by using the above organosilicon compound has not been known as well.
Non-patent document 1: Chem. Rev. 95, 1409 (1995)
Non-patent document 2: J. Am. Chem. Soc., 87, 4313 (1965)
Non-patent document 3: Organometallics, 10, 2526 (1991)
Non-patent document 4: J. Am. Chem. Soc., 87, 4317 (1965)
Non-patent document 5: Chem. Lett., 489 (1998)
Non-patent document 6: J. Am. Chem. Soc., 124, 1574 (2002)
Non-patent document 7: Organometallics, 19, 1077 (2000)
Patent document 1: WO 01/10871
Patent document 2: JP H1-98631 A/1989
Patent document 3: JP H1-272633 A/1989